Board Thread:Pokémon Help/@comment-26040378-20161024205442/@comment-25233866-20161028153144

Yeah, it seems that Eevees are all males because they have a very high chance of males (75%) over females (25%), similar to Starter Pokemon. It is possible to attain a female Eevee before in Silvent City, although it required soft resets to get more chances at getting one.

Just trade for a female Eevee and breed for all of the Eeveelutions.